A Content Management System helps manage the creation of highly functional websites without the need for local software other than a web browser and an internet connection. Effectively content is created and published by the user, although some editorial control may be managed centrally.
For a typical small business website a well set up CMS means that content can be frequently updated, without the need for a "webmaster". Setting up the CMS is rather complicated and not all web hosting companies support the on-line technology required yet. Strangely, those that do support the required services often charge less!